In general terms, furnaces such as those commonly installed to heat homes operate by drawing air from the living area through the furnace, heating the air, and returning it to the living area. In some heating systems, the air drawn from the living area is also used for combustion before being vented to the outside. Other systems draw air for combustion from the outside. Duct systems are generally used to move the air, both heated and unheated, from one location to another. A blower forces the air drawn from the living area for heating through at least one heat exchanger. Usually, more than one heat exchanger is utilized. The heat exchangers are heated by combustion product gases generated by burners in a burner assembly aligned with the inlet to each heat exchanger. The burners receive fuel via a suitable fuel conduit, such as a manifold having orifices that direct the gas into the burners. The gas exiting the burners is ignited by an ignitor provided in a burner box. The burners allow combustion of the gas, as well as direct heated flue gas into the heat exchangers.
The typical heat exchanger includes cells with a channel or pass formed in each cell to direct the flow of flue gas produced by combustion and can be formed from sheet steel ("clamshell" exchangers) or steel tubing ("tubular" exchangers). These cells are typically positioned side by side in a parallel manner and include a predetermined spacing to allow the blower air to flow around the cells. The blower air is thus heated by convection as it circulates over the cells.
The flue gases are typically withdrawn from the heat exchanger by a draft inducer blower and ducted to the outside via a vent duct.
Mobile home furnaces are usually of the down-flow type, that is, the conditioned air ductwork is located below the space where the furnace is installed. Furthermore, known mobile home furnaces utilize drum-style heat exchangers, which are adequate for their purpose. However, it is preferred to utilize multipass clamshell type residential furnace heat exchangers. The size limitations of the mobile home closet, however, have not to date permitted the inclusion of these types of heat exchangers in a furnace design. Whereas a typical (residential) gas furnace for a standard home is approximately 28.5" deep, due to size constraints it is preferred that a mobile home gas furnace be typically 24" deep to fit within a specific closet. A multipass clamshell or tubular heat exchanger is typically about 18" deep, thus leaving 10" for a burner assembly in a typical residential gas furnace and only 6" for a burner assembly in a mobile home furnace. To date, and due to the above size constraints, a down-flow furnace design having clamshell or tubular heat exchangers, as described in the foregoing, has therefore not been available for use in a mobile home.